Such a cooking apparatus and such a cooking unit are known from GB 1 273 023.
In the known cooking unit, the lamp vessel of the IR lamp is bent circularly but for the end portions extending parallel to each other. The advantage of such a lamp vessel is that a hot plate under which the unit is arranged is heated during operation over a surface area of the size of a cooking position more uniformly than with a linear tubular lamp.
A disadvantage of the known IR lamp is that the lamp is fairly expensive due to a time-consuming manufacturing step, in which the lamp vessel or a tube from which the lamp vessel is to be formed is bent. When bending a finished lamp having a lamp vessel sealed in a vacuum-tight manner, there is a risk that the lamp vessel is unintentionally deformed due to the fact that the gas pressure in the lamp vessel increases as a result of temperature increase. The increased temperature required for bending the lamp vessel must therefore be brought about only in the short zone traversing slowly the whole lamp vessel, while the already bent part is being cooled. Since for IR lamps mostly glass is used having a comparatively high softening temperature, for example glass having an SiO.sub.2 content of at least 95% by weight, such as, for example, quartz glass, the step of bending the lamp vessel is time-consuming.
Also if a glass tube from which a lamp vessel is to be formed is circurlarly bent before the lamp is assembled, the bending step is time-consuming, though to a smaller extent than if a finished lamp vessel is bent. The tube can be brought in one step to the required high temperature throughout its length between the end portions. A disadvantage of a bent still open lamp vessel, however, is that a filament provided with supports to keep the filament in a centered position in the lamp vessel at a certain distance from its wall can be introduced only with difficulty into such a lamp vessel. The supports then in fact act as barbed hooks, which impede the introduction of the filament.